Cardiac arrest is the sudden, abrupt loss of heart function. Death usually occurs within
minutes unless cardiopulmonary resuscitation (CPR), rapid defibrillation, and paramedic interventions
are available. CPR consists of pumping on the patient's chest and delivering breaths to produce some
circulation until the heart can be restarted. When the chest is compressed, oxygen-rich blood is pumped forward.
When the chest is released, oxygen-poor blood is brought back to the heart and lungs where it
can be restored with oxygen before being pushed out to the body with another compression.
Both actions -- pushing oxygen-rich blood forward and bringing oxygen-poor blood back to
the heart and lungs -- are important. CPR however produces only about 30% of normal circulation.
Methods to improve the circulation produced by CPR may lead to better survival.